Slave flash trigger for digital camera


It is not easy to connect an external flash to many digital cameras. One way to use an external flash is to use a slave trigger. But the problem is that most digital cameras use a pre-flash to set the white balance before the real flash goes on. That's why the slave flash has to trig on the second flash.


In my pre flash trigger I use a 74HC74 (Dual D-type flip-flop with set and reset; positive trigger) as a counter.
When the first flash comes the clock signal goes high and the signal from D1 come to the output Q1. Q1 is connected to the input D2 so on the second flash the signal on D2 comes to Q2 and trig the thyristor. The complement outputs Q1' and Q2' are connected to a reset circuit. It discharges the 4.7uF capacitor via a 33 kOhm resistor and the whole circuit resets after a while and get ready for the next photo.




5V = four AA batteries will work just fine

Phototransistor = BPW40 (others might work fine but maybe you had to change the 470 Ohm resistor. It should have less then 1 volt over the resistor in normal indoor light)

Thyristor = 2N5064 (any thyristor should work but it should have the Gate Trigger Current about 0.2mA)

Diodes = 1N4148 (any small signal diode should work)









Some useful links:
http://www.leesoft.com/d600l/OlympusFAQ.html
http://www.srelectronics.com/
http://www.kety.home.pl/arten/

A good supplier for electronics (Sweden only):
http://www.labbelektronik.nu

If you have any questions or suggestions for improvements you can send me an email:


My photoalbum here